A tunnel from the 1800s. WWII Strategy. A mushroom farm.

This cache will have you trek through the 1550m long Otford tunnel, marvelling at the graffiti, watching every step and climbing the North gate. Don't forget a torch.

History – Otford Train Tunnel

The Otford Tunnel, carved through the Illawarra escarpment in 1888, was once part of the South Coast railway line connecting Sydney to Wollongong. At over 1.5 kilometres long and with a steep gradient, it quickly earned a reputation as a dangerous passage. Steam trains struggled through the narrow, unventilated tunnel, often filling with smoke and heat, leaving passengers and crew gasping for air. The conditions were so severe that some travellers reportedly fainted from asphyxiation. In an attempt to address this, a vertical ventilation shaft was later added partway along the tunnel to help disperse the smoke. By 1920, the tunnel was decommissioned in favour of a safer route, but its dark, smoky legacy remains a haunting piece of NSW rail history.

History – World War II

During World War II, fears of a Japanese invasion prompted the Australian military to implement a scorched earth policy to deny advancing enemy forces access to key infrastructure. As part of this, in 1942, the Otford Tunnel was targeted for demolition. The idea was to render the route unusable in case of occupation. Explosives were placed at the northern entrance of the tunnel, but the resulting blast did not fully collapse the structure. Instead, it caused only partial damage, leaving the tunnel largely intact. Today, the scorched brickwork and warped steel around the entrance still bear the scars of that wartime decision.

History – Mushroom Farm

After its closure to trains, the Otford Tunnel found a second life in the 1980s when local mushroom farmers began using it for cultivation. The tunnel’s constant cool temperature and high humidity made it ideal for growing fungi. Farmers set up racks and irrigation systems inside, using a small tractor to haul materials in and out. Though the operation eventually ceased, remnants of this era still remain: rusted machinery parts and scattered debris, now sit abandoned at the northern entrance, quietly marking the tunnel’s unlikely agricultural chapter. You will even notice an abandoned tractor halfway through the tunnel (GCCA6). 

Cache Information

Access

This cache is located on the gate at the Northern entrance of the tunnel. Due to accessibility, I highly recommend you start at the Southern end of the tunnel (in Waypoints) and walk the length (1550m). Allow about 30 minutes for this walk each way. Parking is recommended at Chellow Dene Avenue (WPs). There is no reception within the tunnel, so I recommend PRE-LOADING this page. Go with someone, or at the very least tell someone where you are going. 

Gear

To safely travel through the tunnel, you WILL require a torch. A phone flashlight simply will not do. It is urged that you bring at least 2 torches, as a backup in case the first one dies (which happened to me). It is quite cold in the tunnel due to breezes which come through, so bring a jacket. The tunnel has water flowing through it, so I recommend gumboots. 

 Cache

The cache is a magnetic bison tube, hidden at the top horizontal beam of the gate. The gate is about 15m from the end of the tunnel. You will need to climb the gate. See the photo below for reference. Please return to the exact position, so that muggles will not spot this cache. 

Gallery

Metal Gate Where Cache Resides. 

Portrait Alley – Selection of Artworks

Southern Entrance circa 1900s